Articles having polished surfaces



Jan. 10, "1928'.

C. A. NASH ARTICLES HAVING POLISHED SURFACES Filed July 1. 192];

INVENTOR. 10W 0 W ATTORNEY Patented Jan. 10, 1928'.

mural) STATES PATENT OFFICE.

CLARENCE A. NASH, OF MILWAUKEE, WISCOIQ'SIN, ASSIGNOR TO THE CUTLER-HAM MER MFG. 00., OF MILWAUKEE, WISCONSIN, .A CORPORATION OF WISCONSIN 7 ARTICLES HAVING POLISHED SURFACES.

Application filed July 1, 1921. Serial No. 481,748.

This invention relates to articles having polished surfaces, particularly articles formed of plastic compositions, and to a method of constructing or producing articles having surfaces so polished.

Many articles, particularly those formed of plastic compositions as, for example, the insulating parts of various electrical devices require a finish and high polish. However,

10 such plastic compositions, especially when molded and subjected to a heat treatment are very difficult to finish as desired which characteristic has led to the use of surface coatings adapted to take a better finish but 5 such coatings as heretofore treated have notv proven entirely satisfactory. I

The present invention has among its objects that of providing an article so constructed as greatly to facilitate the desired finish thereof.

Another object is that of providing articles so constructed as to materially improve the lustre, density and water resistivity of the finishedv surfaces thereof.

Another object is that of providing a simple and expeditious method of constructing articles having surfaces which exhibit the foregoing characteristics.

Other objects and advantages will hereinafter appear.

According to the present invention it is proposed to construct the article with a surface layer of fusible material to be subjected to both a heat treatment and a smoothing and polishing treatment.

Preferably the article soconstituted is subjected to a heat treatment preferably after partial butting thereof. The temperature to which the aforementioned article is so subjected preferably substantially equals or somewhat exceeds that at which the fusible surface layer is adapted to soften, it having been found that the surface of, the coating may thereafter be re-polished to produce a finish superior in brilliancy, durability and water resistivity to thatobtainable by usual methods.

Referring to the accompanying drawing which illustrates one embodiment of the invention, the same shows an attachment plug cap comprising a molded insulating body 1 and a surface layer 2. j

The body 1 may comprise any preferred composition such for example as the well known composition including a comminuted asbestos filler and pitch binder. In practice such a base is commonly cold molded While plastic and baked until render-ed very hard, the resultant product being inadapted totake a satisfactory finish.

The surface layer 2 may comprise any one of numerous fusible plastic compositions as for example one composed of coal tar pitch, substantially parts, and finely divided silica -o r flint, substantially 40 parts. The proportions may vary between somewhatwide limits and are also infiuenced'by the character of the finish desired, whereas numerous other substances or compounds may be employed as finishing material for such or other classes of pieces.

As a specific example of the instant method the following steps may be mentioned.

A body composed of a base material such as that described is treated to provide the same with a fusible surface layer of mate rial such as that mentioned, which treatment may be effected preferably by bufiing'. In practice the material for such surface layer is preferably or conveniently applied directly to the surface of-the bufiing wheel or other smoothing device employed and thence transferred to the surface of the piece during the buffing or smoothing operation.

Such operation is preferably continued until a reasonably smooth and glossy exterior surface is obtained. The piece, having the fusible surface layer thus formed thereon, is thereafter subjected to heat treatment at a temperature preferably approximating or somewhat higher than that at which fusion of the surface layer or of the more readily fusible surface portions thereof, takes place.

The duration of such heat treatment may I vary from somewhat less than half an hour to two hours or longer, dependent upon the size and shape of the piece and the character and consistency of the surface material thereof. It is also desirable that such treatment be'continued long enough to eflect thorough softening of the surface material Without causing the latter to run, whereas, obviously such treatment should not be so long continued, or carried out at such temperature, as. to injure the base material. Following such treatment the piece is permitted to cool sufficiently to effect setting or hardening of v,the surface material and is thereafter again polished either while still somewhat warm or at ordinary temperature. Such second polishin operation is preferably effected also by iiufling, the surface employed being preferably somewhat softer and more yielding than that employed during the first operation.

Such second polishing operation may be effected either with or without addition of a fresh surface material but in either case if the same instrumentality be employed for several pieces consecutively its surface will ordinarily become to some extent covered or impregnated with such material.

The finish of pieces subjected to the complete treatment aforedescribed is found to be superior to that of pieces polished only by ordinary methods in the aforementioned rcspects among others.

A surface material such as that aforedescribed is adapted to soften'at a temperature of approximately 180 to 200 F., dependent upon the constituency of the coal tar pitch employed, and the heat treatment where such compound is employed should be carried out preferably at a temperature which may vary between 180 and 250 F. However, such temperature should preferably be high enough to effect softening and substantial fusion of the surface material, or of its more readily fusible constituents without causing the latter to run off or separate from the base material.

Without limitation to, any particular theory in accounting for the very marked improvements resulting from the aforedescribed process of construction, it is believed that where coal tar pitch or an analogous composite substance is employed as one of the principal constituents of surface material such coal tar pitch undergoes distillation during the heat treatment, the more volatile constituents thereof being driven off leaving a residue which is much harder and denser and hence better adapted to receive and retain a high finish than is the material prior to such treatment. Further it is believed pores of the body as well as fill all depressions or minute cavities in the surface therer of, whereby the tenacity of adhesion of the ceedingly smooth film of its own substance,

due probably to the high surface tension of the softened material, which smoothness re- -mains after cooling and consequent hardening, whereas the final polishing treatment should be so effected as not to remove or impair such characteristic of the surface.

Thus, as a result of the aforedescribed construction the articles produced thereby are characterized by exceedingly close and firm amalgamationof the surface material as compared with similar pieces polished only by ordinary methods. Also the final finish of pieces produced as herein set forth is markedly superior in brilliancy, water re- .sistivity and permanence to pieces produced by ordinary methods.

It is, of course, to be understood that deviations from the aforesaid method may be made without departing from the scope of desire to secure 3. The method of polishing surfaces of I plastic composition articles, by impregnating with a fusible material and smoothing, which comprises, application of said material by buffing and, as a distinct step, heat softening with subsequent resetting of the surface material in situ thereof.

4. The method of constructing articles having polished surfaces, which comprises providing the same with a surface layer of thermoplastic material which is capable of heat hardening, thereafter softening the surface material by application of heat, continuing the heat treatment for effecting volatilization and expulsion of constitutents of the material to thereby increase the hardness of such material when cold, terminating the heat treatment to provide for setting of the surface coating, and polishing the latter.

5. The method of constructing articles having polished surfaces, which comprises providing the article with a surface layer of a fusible material capable of heat hardening, smoothing the exterior surface of such material, subjecting the article including such surface layer to heat treatment for thorou h amalgamation of the surface layer with t e body of the article and also for fusion and ultimate hardening of the surface material prior to final smoothing and thereafter again smoothing the surface of such'material. 9

6. The method of constructing articles having polished surfaces, which comprises forming upon the piece a surface layer of plastic finishing material having volatile constituents and smoothing the surface of such material; heating the article to effect amalgamation of said surface layer therewith and to expel certain of the volatile constituents of said surface material for hardeningth'e residuum, and smoothing the surface of the material so hardened.

7. The method of constructing an article having a smooth surface of fine texture,

l which comprises applying to a cold molded and baked article of plastic material a surface layer of .coal tar pitch and a finely'divided relatively infusible substance, and thereafterheating said surface layer to amalgamate it with the article to increase the surface density thereof.

8. The method of providing a smooth and dense surface on a cold molded and baked article of plastic composition, which comprisesapplyingto sai article b buffing a layer of coal tar pitch and finely ivided silica, thereafter heating said article to effect CLARENCE A. NASH.

have hereunto sub- 

